1. Field of the Invention
In one respect this invention relates to braking mechanisms. In a further aspect, this invention relates to chain hoists, especially lever driven hoists.
2. Prior Art
In its most general form the brake of this invention can be used as a safety brake on various lifts and hoists. Many countries and their subdivisions require cranes and lifts to have some safety means for preventing a load from dropping in an uncontrolled manner. Prior art brakes are usually responsive to the acceleration of a dropping load. Such brakes can allow the load to attain a substantial speed where the acceleration is low creating a dangerous uncontrolled load.
One example of hoists is the lever driven chain hoists known in the art. One example is shown in U.S. Pat. No. 3,047,114. In general the prior art lever driven hoists devices have a housing which contains drive means. Power is furnished to the drive means by a lever. The drive means can be set so as to draw or release a load attached to a chain passing through the hoist. Generally the hoist is used to raise and lower loads vertically. When it is desired to move the chain without using the lever the hoist can be set in a free chaining mode which allows the chain to be pulled rapidly through the hoist.
Free chaining allows a rapid movement of the chain but has consequent dangers. If a load is inadvertantly applied or the operator is careless, the chain can move rapidly through the hoist allowing the load to fall in an uncontrolled manner. To solve this problem some prior art hoists are equipped with a brake which is sensitive to acceleration. If the load on one of the prior art hoists suddenly accelerates a braking mechanism is applied and stops the load. However, if the load accelerates slowly it can achieve a substantial velocity without activating the brake. Therefore, even though the risk of injury is lessened, a substantial risk of injury still exists.